The present invention relates to a disk drive unit and a disk device having this drive unit, and more particularly to a hydrodynamic fluid bearing unit for the disk drive unit.
Recently, in order to achieve the high-speed transfer of data and high-density recording, a motor in a magnetic disk drive unit has been more and more required to achieve a high-speed, high-precision rotation. In order to meet this requirement, a motor (as disclosed in JP-A-5-336696, JP-A-8-189525 and JP-A-9-200998), having a hydrodynamic bearing, has been proposed.
A motor in a magnetic disk drive unit is intensely required to have an improved shock resistance so that the function of the disk drive unit will not be deteriorated when a personal computer, incorporating the disk drive unit, is dropped from a desk or is fallen while it is carried.
Particularly, a notebook-type personal computer can undergo an impact force of about 1,000 G while it is used or carried, depending on the manner of handling it. And besides, since the notebook-type personal computer is driven by a battery, it requires a disk drive unit of the low power consumption-type.
A groove bearing, wherein shallow grooves for producing a dynamic pressure are formed in a spindle, is proposed in JP-A-5-336696. Although this groove bearing is excellent in high-speed operation and in accuracy of the spindle rotation, it has problems that the production cost is high and that the mass production can not be easily carried out. The depth of the dynamic pressure-producing grooves in the groove bearing are several microns, and when the grooves are deformed by an impact load, the adequate dynamic pressure cannot be produced, which results in a possibility that the unstable vibration occurs. A hydrodynamic three-lobe bearing, disclosed in JP-A-8-189525 and JP-A-9-200998, can achieve high-speed, high precision rotation equivalent to that obtained with the above groove bearing. However, when an impact force of about 1,000 G acts on this bearing, edge portions of the grooves can be deformed, so that its bearing characteristics are deteriorated.
JP-A-8-189525 discloses a groove-type thrust bearing. When a bearing surface of the groove-type thrust bearing is deformed by an impact force, it is liable that a lubricating fluid is not properly supplied to the bearing surface.
The groove-type bearing supports or bears a thrust load at an end surface of a spindle or bearing, and therefore is subjected to a larger friction loss as compared with a ball bearing-type, and it is difficult to achieve a low power consumption design.